The present invention relates, in general, to a method for determining air-bridge post placement and, more particularly, to a method for determining air-bridge post placement in the production of gallium arsenide type semiconductor devices.
In producing large scale semiconductor devices, it is necessary to provide interconnecting lines between various discrete devices within the large scale device. As the number of discrete devices increases, the number of interconnect lines increases, often exponentially. The formation of interconnect lines is typically accomplished using at least two layers of metal. The conducting lines running in one direction (vertically) are placed on the first layer and the lines running perpendicular to the first lines (horizontally) are placed on the second layer.
The discrete semiconductor devices are generally organized in cell rows with channels disposed therebetween for the interconnect lines. Areas in the cell rows, called feedthroughs are provided for the passage of interconnect lines that must pass over, or through, a cell row. These feedthroughs may also be provided within a cell.
Typically, the interconnect lines will be deposited on an oxide substrate. However, a gallium arsenide (GaAs) device's frequency of operation is limited typically by the capacitance on its critical metal interconnections. Since the dielectric constant of air is lower than that of oxide, the second metal interconnect layer in gallium arsenide is preferably a gold air-bridge suspended on posts above the substrate and the oxide.
Because of the weight of the interconnect lines and the lack of support between connecting posts, it is often necessary to place intermediate supporting posts. Leaving room for these intermediate posts can pose substantial layout problems when designing a circuit.
Accordingly, it is an object of the present invention to provide a method for determining air-bridge post placement that overcomes the above deficiencies.
A further object of the present invention is to provide a method for determining air-bridge post placement which may be implemented utilizing computer aided design equipment.
Another object of the present invention is to provide a method for determining air-bridge post placement which will minimize the number of posts utilized.
Still another object of the present invention is to provide a method for determining air-bridge post placement which minimizes the area expansion to make room for the required posts.